The present invention relates to a wireless communication system, for example, to a resource assignment method and a communication apparatus that implements the method in a cellular wireless communication system that employs the Orthogonal Frequency Division Multiplexing method.
As broader band wireless communication becomes more and more popular, the multicarrier communication method has become increasingly used in which transmission information is divided into multiple frequency bands, called subcarriers, for use in communication. The OFDM (Orthogonal Frequency Division Multiplexing) method, one of the multicarrier communication methods, is widely used in many systems because the OFDM method uses the narrowed bandwidth of each subcarrier to increase resistance to delayed waves and, at the same time, makes use of signal orthogonality to eliminate the need for the guard bands between subcarriers for higher frequency usage efficiency. In addition, OFDMA (Orthogonal Frequency Division Multiple Access) method, in which the OFDM radio resource is divided into units, hereinafter called resource blocks, each having one or more subcarriers and a predetermined time width for realizing multiple access, is employed in a system called WiMAX (Worldwide Interoperability of Microwave Access) and a system called LTE (Long Term Evolution).
For example, 3rd Generation Partnership Project: TSG RAN; E-UTRA; Physical Channels and Modulation (Release 8), 3GPP TS 36.211 V8.6.0, March 2009 describes radio resource division and the modulation method in LTE. The document describes the OFDMA method in which, for downlink data communication from a base station (BS) to a mobile terminal (MT), the modulation signal for each user is assigned directly to the time and the frequency resource. The document also describes the SC-FDMA (Single Carrier-Frequency Division Multiple Access) method in which, for uplink data communication from a mobile terminal to a base station, the modulation signal for each user is once converted via DFT (Discrete Fourier Transform) and then assigned to the time and the frequency resource.
In those radio communication methods, the ICIC (Inter-Cell Interference Coordination) technology is used that limits the resources used for each cell in order to reduce inter-cell interference. For example, JP-A-2008-530918 discloses the technology for using different frequencies according to the location of a mobile terminal in a cell in order to reduce inter-cell interference.
Because the load status, such as the number of mobile terminals or the amount of communication, differs among cells and changes over time, fixed limitation on the resources would generate an imbalance in the usage status of resources in each cell. To prevent this imbalance, a method is proposed for dynamically coordinating the resource limitation by exchanging load information among cells. 3rd Generation Partnership Project: TSG RAN; E-UTRAN; X2 application protocol (X2AP) (Release 8), 3GPP TS 36.423 V8.5.0, March 2009 standardizes, as the load information exchanged among cells, the following information for the X2 interface that is the interface between base stations: UL Interference Overload Indication indicating the interference level received by a base station for each resource block, UL High Interference Indication indicating the sensitivity to interference for each resource block from each neighboring cell, and Relative Narrowband Tx Power indicating the transmit power information for each resource block from the base station.